Pivmecillinam has the antimicrobial activity of mecillinam to which it is hydrolysed in vivo. It interferes with the synthesis of bacterial cell wall. It is active against many gm-ve bacteria, esp Enterobacteriaceae including Escherichia coli, Enterobacter, Klebsiella, Salmonella and Shigella spp; indole-positive Proteus and Serratia marcescens are resistant. It is inactivated by beta-lactamases, but is more stable than ampicillin.